feat(#3): Add namespace support

[nyetwurk]

Description

Adds namespace support to use same bucket for several different uploaders.

Fixes #3

Type of change

Please delete options that are not relevant.

• New feature (non-breaking change which adds functionality)
• This change requires a documentation update

How Has This Been Tested?

Not tested yet

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

[nyetwurk]

We don't need this if s3_bucket can be something like "solana-snapshots/mainnet" or even "solana-snapshots-mainnet"